The depolarization field effect on the thin ferroelectric films properties

The calculation of the spontaneous polarization (P-s), dielectric susceptibility (chi) and pyroelectric coefficient (Pi) of the ferroelectric films has been performed in the phenomenological theory framework. Euler-Lagrange equation was solved analytically under the boundary conditions with different extrapolation lengths at two surfaces, respectively. The depolarization field contribution was taken into account in the model of short-circuited mono domain ferroelectric film, treated as perfect insulator. The detailed analysis of the aforementioned quantities' space distribution and their average values in two cases with and without depolarization field was carried out. It was shown that the depolarization field shifts critical temperature to smaller value and critical thickness to bigger value in comparison to those obtained without accounting for the depolarization field, this shift being larger the smaller the extrapolation length values. This phenomenon is related to the different thickness dependence of the critical temperature, namely T-c - T-cl similar to 1/l or T-c - T-cl similar to1/l(2) with and without depolarization field contribution correspondingly. Meanwhile average values of P-s, chi and Pi are similar in both cases. The depolarization field was shown to flatten P-s, chi and Pi space distributions, which have the peculiarities otherwise (e.g. small maxima in chi and Pi coordinate profiles near the film surfaces). It was shown that depolarization field influence in a short-circuited film could be neglected when the film thickness or the extrapolation lengths in the boundary conditions are larger than correlation length value. (C) 2002 Elsevier Science B.V. All rights reserved.